Biogenic Fe Incorporation into Anaerobic Granular Sludge Assisted by Shewanella oneidensis MR-1 Enhanced Interspecies Electron Transfer and Methane Production

Abstract

Incorporating conductive Fe into matured anaerobic granular sludge (AGS) through a biologically induced mineralization process is a promising approach to enhancing methane (CH4) production. In this study, much more biogenic Fe was formed and immobilized in AGS assisted by Shewanella oneidensis MR-1 (S-Fe-AGS), aimed to enhance the interspecies electron transfer (IET) and CH4 production. Results showed that the CH4 production of S-Fe-AGS was, respectively, enhanced by 53.92 and 30.79% compared to that of pristine AGS and Fe-loaded AGS without Shewanella oneidensis MR-1 supplementation. Multiple electrochemical characterizations indicated that the incorporation of biogenic Fe could not only increase the capacitance and conductivity of AGS but also enhance the electrochemical activity of extracellular polymer substances (EPSs). These could facilitate the direct IET between methanogens and syntrophic acidogens in AGS. In addition, the incorporation of biogenic Fe also increased the production of redox-active substances in EPS and the abundance of Bacteroidota, Syntrophobacter, and Methanosarcina in S-Fe-AGS. All these factors could jointly contribute to an improved IET process and subsequently promoted CH4 production. This study provided a biosynthesis strategy coupled with bioaugmentation to promote the IET process and energy recovery of AGS.